U2 



found minutely to coincide with the distance previously mea- 

 sured upon the bank.* 



From these experiments I am persuaded that this con- 

 struction of wheel is well adapted either for registering 

 continuously the progress of a vessel through the pathless 

 deep, or for ascertaining at intervals, as a substitute for the 

 common log, what is the rate of sailing at the time of 

 observation. For the latter purpose a small wheel one foot 

 in diameter would be sufficient, attached to the side of the 

 vessel, so contrived as to be let into the water or withdrawn 

 at pleasure. The motion of the wheel might readily be 

 transmitted by a rod, working in a tube to an index near the 

 observer upon deck. 



But the very powerful tendency which these wheels possess 

 of rotating upon their axes when placed in a stream of water, 

 show that they admit of very extended application. Not 

 only will they be found an improvement upon the common 

 windmill sail where a defect in construction, in consequence 

 of the elastic nature of the moving power, cannot be easily 

 detected, but they may be advantageously substituted for 

 the undershot water-wheel, in rivers and situations where 

 there is greater depth of water than can be made to act upon 

 the floats of such wheels. The undershot water-wheel can only 

 be advantageously immersed in the stream to the depth of a 

 certain proportion of its radius ; to increase, therefore, its 

 power, its bulk must be increased in an extraordinary degree. 

 These wheels, on the contrary, admit of any depth of imraer- 



* I have since made others of a very delicate construction, and have found 

 them calculated to measure with tolerable accuracy the velocity of the wind or 

 the currents of air through mines ; to these I have attached wheel-work to register 

 the current v/hich had passed through them up to 1,000,000 feet. I had also 

 contrived an apparatus^ to be attached thereto, so that not only the velocity of the 

 air at the time of observation could be registered, but the machine itself would 

 register what had been the velocity at any period during the interval of a week. 

 In this apparatus, however, I have reason to suppose, I have been anticipated by 

 a gentleman who has recently taken out a patent for a similar invention. 



I 



